Insulin binds to cell membrane. Technics employing gradient centrifugation for the preparation of relatively pure plasma membranes are now available. The effect of different factors on the binding of insulin to such preparations will be investigated. The effect of insulin on the enzyme activity of such preparations will be determined. Previous studies on the effect of insulin on protein and nucleic acid metabolism are continued with particular emphasis on kinetic changes in precursor specific activity. A study of the modification of insulin effect by thyroid hormones will also be carried out. Further studies testing the hypothesis that some of the effects of insulin result from its inhibition of adenyl cyclase will be performed.